A. Field of the Invention
The present invention relates generally to the field of tooling for punch presses, and more particularly to adjustable-length punch assemblies for punch presses wherein the punch assembly may be adjusted to compensate for losses in punch blade length as a result of sharpening.
B. Description of the Prior Art
In punching operations, the distance between the sharpened edge of the punch tip and the workpiece is a critical dimension. When a dulled punch tip is reground to restore a sharp edge, material loss changes this critical dimension. To account for this, adjustable punch assemblies that allow punch length adjustment have been developed.
U.S. Pat. No. 4,375,774 discloses an adjustable punch assembly wherein a punch (12) is carried by an axially guided punch driver (13), which in turn is threadably mated with a punch head or cap (14), whereby punch length is adjustable by rotating the punch cap relative to the punch driver. An expandable locking dowel pin (58) is wedged in aligned holes (59) in the punch cap and punch driver as a releasable locking means for preventing relative rotation between the punch cap and punch driver. The locking pin must be temporarily removed by the operator to enable length adjustment.
Another adjustable punch assembly is described in U.S. Pat. No. 5,131,303. The described punch assembly includes a punch (20) threadably mated with a punch driver (10) to enable axial length adjustment by relative rotation of the mating parts. As shown in FIGS. 4 and 5 of this patent, a C-shaped spring clip (30) having a radial protrusion (39) at one end thereof fits within an annular groove (31) in the mating end of the punch driver, and protrusion (39) extends through a radial aperture (33) for receipt within a V-shaped recess 32 in the punch. The spring clip 30 is constrained in a locking position by an outer punch guide (40), which must be temporarily removed for sharpening and punch length adjustment.
U.S. Pat. No. 5,329,835 teaches an adjustable punch assembly having a pushbutton releasable locking means (50) operable along the central axis of the punch assembly. More specifically, a punch cap (26) is threadably mated with a tool-holding punch driver (14), and push button (50) includes four comer detents (55), (57), (59), and (61) normally engaged with four corresponding detent stops from a plurality of circumferential detent stops (70) in the punch cap (26) and also engaged with four corresponding detent stops (55'), (57'), (59'), and (61') in the punch driver. The push button can be depressed in an axial direction against the bias of a spring to disengage the comer detents from the detent stops (70), thereby releasing the punch cap for adjustment rotation relative to the punch driver.
A more recent adjustable punch assembly is disclosed in U.S. Pat. No. 5,647,256. The disclosed punch assembly includes a punch cap (28) threadably mated with a punch driver (18) to permit length adjustment by rotating the parts relative to one another. A spring seat (32) is provided coaxially with the punch cap and punch driver adjacent the punch cap, and a releasable securing member (38) prevents relative rotation between the spring seat and the punch cap to indirectly prevent adjustment rotation between the punch cap and punch driver. The releasable securing member is radially depressible against a spring bias to uncouple the punch cap from the spring seat to enable adjustment rotation between the punch cap and punch driver.
The prior art adjustable punch assemblies mentioned above are complex to manufacture and/or require some disassembly to carry out length adjustment.